The present invention relates to a method of forming a fluorescent screen of a black matrix type color picture tube and, particularly to a method of forming a mosaic or stripe pattern film, i.e. so-called black matrix film, of light absorptive material.
In general, in a black matrix type color picture tube, there are provided trios of red, green and blue phosphor dots or stripes arranged in a predetermined pattern on the inner surface of a glass panel, and the gaps among the phosphors are covered with a film of a light absorptive material such as graphite. Conventionally, the fluorescent screen having the above-mentioned structure was generally formed through photolighorgraphy process.
Namely, as disclosed in U.S. Pat. No. 3,558,310, for example, a thin photosensitive or light-hardenable resin film is first formed on the inner surface of a face plate. Next, the photosensitive resin film is exposed to light through a shadow mask so as to harden the portion of the photosensitive resin film where phosphors are going to be applied. Then, unexposed portion of the photosensitive resin film is removed by developing using a hot water spray or the like, so that only the exposed portion corresponding to the phosphor applying portion of the photosensitive resin film remains. Here, the unexposed portion includes the portion which is not hardened completely due to an insufficient exposure to light. After that, the inner surface of the face plate bared by developing corresponding to the unexposed portion and the entire surface of the left behind hardened film (exposed portion) are applied with a slurry of graphite as a light absorptive material, and a graphite film is formed. Next, the left behind hardened film portion of the photosensitive resin film corresponding to the phosphor applying portion is swollen and rendered fragile using an exfoliating agent, and the hardened film portion of the photosensitive resin film and the graphite film formed on it are removed by a hot water spray and thus, the graphite film is partly perforated so that corresponding portion of the face plate is bared for formation of a black matrix film. After that, phosphor is applied into the opening formed in the black matrix film in a manner well known in the art, and after filming an aluminium reflective film is deposited to complete a black matrix fluorescent screen.
However, the foregoing method of forming a black matrix fluorescent screen is complex and needs many steps including application of photosensitive resin, exposure of light, development, application of light absorptive material, exfoliation process, and development in order to once form a hardened photosensitive resin film and then to remove it. It also requires an exfoliation process using an oxidizing agent such as hydrogen peroxide or alkalihypochlorite for removing the exposed portion of the photosensitive resin film, raising disadvantages in handling dangerous processes. Also, the oxidizing agent rusts other components such as the shadow mask, and they remain in graphite even after the fluorescent screen has been completed. Moreover, the waste exfoliating agent must be treated so as to avoid evironmental pollution.